VERIFICATION - Modest Lake-Effect Snow Event: 23-24 November 2012

A modest lake-effect snow (LES) event occurred this past weekend across the Great Lakes. The 72-h snowfall ending 25 November 2012 at 1200 UTC (image below) shows the COOP and CoCoRaHS snowfall reports in this area. For the most part amounts were relatively light, however the favored LES areas across the Upper Peninsula (UP) of Michigan, northern Lower Michigan, and southwestern New York received more than 6" of snowfall.

Some of the analog impact guidance that was referred to in a blog post last week (located here) is shown below.

Based on the GFS 96-h forecast leading up to the event, the analogs were suggesting that this would not be a widespread or heavy LES event and the favored areas downwind of the lakes would have the most impact. In the mean and probability snowfall guidance, the highest totals (6-8") and probabilities of > 6" of snow (50-60%) were located in the UP of Michigan near the Keweenaw Peninsula where 8-12" of snow was common. Although the analog guidance mean snowfall amounts can be "underestimated" due to a few non events being incorporated into the mean, it is easy to determine which areas are potentially most susceptible in the upcoming event by analyzing the probability threshold maps. The probabilities of >6" of snowfall were >30% in the locations that received >6" of snowfall.  In addition, the probability guidance also shows how using higher thresholds can provide an upper limit to the impacts based on the conditional climatology of the upcoming forecast. In the probability map of >12" of snowfall (shown below), >30% probabilities were non-existant across the Great Lakes.